美国的配水系统通常携带氯残留量小于0.05 mg/L，且始终携带氯残留量大于0.1 mg/L。本文概述了使用氯作为消毒剂残留的一些好处，并考虑了支持该应用的系统特征（系统年龄和脆弱性）。保持余氯的益处包括防止适度程度的污染物侵入，充当此类污染物存在的哨兵，以及降低异养生物生长的可能性。包括17个参考文献、表格、图表。

Water distribution systems in the United States routinely carry chlorine residuals < 0.05 mg/L and invariably carry residuals > 0.1 mg/L. This article outlines some of the benefits of using chlorine as a disinfectant residual and considers system characteristics (system age and vulnerability) that support this application. Benefits accruing to maintenance of a chlorine residual include protecting against modest degrees of intrusion of contaminants, serving as a sentinel for the presence of such contamination, and reducing the potential for growth of heterotrophic organisms. Includes 17 references, tables, figures.